Devices for distributing drive forces to the left and right driving wheels of a vehicle have been proposed. In one example of a left/right drive force distribution mechanism of a vehicle, the revolving speed of one of the left and right driving wheels is output after being increased or decreased by a predetermined change gear ratio; which output portion is then engaged with the other one of the left and right driving wheels, thereby transmitting drive torque from the faster revolving side to the slower revolving side. For example, if the revolving speed of one of the left and right driving wheels is increased and output, the revolving speed of this output portion becomes higher than the revolving speed of the other driving wheel during normal running where the revolving speed difference between the left and right driving wheels is small. Accordingly, this output portion is engaged with the other driving wheel, thereby transmitting drive torque from the one driving wheel on the faster revolving side to the other driving wheel on the slower revolving side, thus enabling required distribution of the drive force.
A vehicle incorporates an electronic control brake device, which has an ABS function that ensures braking performance by preventing a wheel from locking during sudden braking or braking on slippery road surface, and a brake assist function that ensures steering operation and vehicle stability. This electronic control braked device also has a TRC function that controls engine output by controlling oil pressure for the driving wheels, suppresses slippage of the driving wheels and ensures not only drive force appropriate to road surface conditions, but also the ability to accelerate from stand still, straight movement, and turning stability. Further, this electronic control brake device has a VSC function designed such that when wheels are at risk of skidding out of control, as in unexpected situations caused by road surface conditions, vehicle speed, sudden turning, or other external factors, engine output and brake control cooperate to reduce such risk.
Therefore, when the drive forces of the left and right driving wheels are distributed by the drive force distribution mechanism of the vehicle, the electronic control system brake device may control the drive of an engine and brake force of a brake. In this case, the electronic control brake device assumes importance, in control of motion of the vehicle, to the moment of the entire vehicle and target values of slip speeds of the driving wheel. This makes it difficult to control the speed difference between the left and right driving wheels, which are distributed by the drive force distributing mechanism.
If brake control, which uses the electronic control system brake device, and drive force distribution control for left and right driving wheels, which uses the drive force distribution mechanism, are simultaneously exerted, the speed difference between the left and right driving wheels increases, making it difficult to obtain a target vehicle behavior.
To overcome such a problem, a proposal has been disclosed in Patent Document 1 described below. In a left/right drive force adjusting device of a vehicle, disclosed in the Patent Document 1, a drive force transmission control mechanism for adjusting drive forces for the left and right driving wheels is disposed between the left and right rotational shafts of the vehicle. If the revolving speed ratio between the left and right wheels exceeds the boundary value at which the revolving speed ratio between the left and right wheels reverses between the output portion side of a transmission mechanism and the other rotating shaft side thereof, this drive force transmission control mechanism stops drive force transmission control exerted by a torque transmission mechanism.
Patent Document 1: Japanese Patent No. 2848126